mtd: spi-nor: Constify struct spi_nor_fixups

'struct spi_nor_fixups' are not modified in this driver.

Constifying these structures moves some data to a read-only section, so
increases overall security, especially when the structure holds some
function pointers.

On a x86_64, with allmodconfig, as an example:
Before:
======
   text	   data	    bss	    dec	    hex	filename
  23304	  13168	      0	  36472	   8e78	drivers/mtd/spi-nor/micron-st.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  23560	  12912	      0	  36472	   8e78	drivers/mtd/spi-nor/micron-st.o

Signed-off-by: Christophe JAILLET <[email protected]>
Acked-by: Pratyush Yadav <[email protected]>
Signed-off-by: Pratyush Yadav <[email protected]>
Link: https://lore.kernel.org/r/aa641732ba707ce3690217825c3ca7373ffde4f9.1748191985.git.christophe.jaillet@wanadoo.fr

Author: tititiou36

drivers/mtd/spi-nor/micron-st.c

@@ -189,7 +189,7 @@ static int mt25qu512a_post_bfpt_fixup(struct spi_nor *nor,
 	return 0;
 }
 
-static struct spi_nor_fixups mt25qu512a_fixups = {
+static const struct spi_nor_fixups mt25qu512a_fixups = {
 	.post_bfpt = mt25qu512a_post_bfpt_fixup,
 };
 
@@ -225,15 +225,15 @@ static int st_nor_two_die_late_init(struct spi_nor *nor)
 	return spi_nor_set_4byte_addr_mode(nor, true);
 }
 
-static struct spi_nor_fixups n25q00_fixups = {
+static const struct spi_nor_fixups n25q00_fixups = {
 	.late_init = st_nor_four_die_late_init,
 };
 
-static struct spi_nor_fixups mt25q01_fixups = {
+static const struct spi_nor_fixups mt25q01_fixups = {
 	.late_init = st_nor_two_die_late_init,
 };
 
-static struct spi_nor_fixups mt25q02_fixups = {
+static const struct spi_nor_fixups mt25q02_fixups = {
 	.late_init = st_nor_four_die_late_init,
 };
 

drivers/mtd/spi-nor/spansion.c

@@ -578,7 +578,7 @@ static int s25fs256t_late_init(struct spi_nor *nor)
 	return 0;
 }
 
-static struct spi_nor_fixups s25fs256t_fixups = {
+static const struct spi_nor_fixups s25fs256t_fixups = {
 	.post_bfpt = s25fs256t_post_bfpt_fixup,
 	.post_sfdp = s25fs256t_post_sfdp_fixup,
 	.late_init = s25fs256t_late_init,
@@ -650,7 +650,7 @@ static int s25hx_t_late_init(struct spi_nor *nor)
 	return 0;
 }
 
-static struct spi_nor_fixups s25hx_t_fixups = {
+static const struct spi_nor_fixups s25hx_t_fixups = {
 	.post_bfpt = s25hx_t_post_bfpt_fixup,
 	.post_sfdp = s25hx_t_post_sfdp_fixup,
 	.late_init = s25hx_t_late_init,