pinctrl: single: Fix potential division by zero

There is a possibility of dividing by zero due to the pcs->bits_per_pin
if pcs->fmask() also has a value of zero and called fls
from asm-generic/bitops/builtin-fls.h or arch/x86/include/asm/bitops.h.
The function pcs_probe() has the branch that assigned to fmask 0 before
pcs_allocate_pin_table() was called

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: 4e7e801 ("pinctrl: pinctrl-single: enhance to configure multiple pins of different modules")
Signed-off-by: Maxim Korotkov <[email protected]>
Reviewed-by: Tony Lindgren <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Linus Walleij <[email protected]>

Author: ProjectMutilation

drivers/pinctrl/pinctrl-single.c

@@ -727,7 +727,7 @@ static int pcs_allocate_pin_table(struct pcs_device *pcs)
 
 	mux_bytes = pcs->width / BITS_PER_BYTE;
 
-	if (pcs->bits_per_mux) {
+	if (pcs->bits_per_mux && pcs->fmask) {
 		pcs->bits_per_pin = fls(pcs->fmask);
 		nr_pins = (pcs->size * BITS_PER_BYTE) / pcs->bits_per_pin;
 	} else {