platforms/blackpill-f4: DFU cleanup

* Reset unnecessary braces change
* Drop last unneeded `#pragma`s
* Add a clarification on reboot flows

Author: ALTracer

src/platforms/common/blackpill-f4/blackpill-f4.c

@@ -131,18 +131,18 @@ const char *platform_target_voltage(void)
 	return NULL;
 }
 
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Warray-bounds"
-
+/*
+ * Write the bootloader flag and reboot.
+ * The platform_init() will see this and reboot a second time into ST BootROM.
+ * If BMPBootloader is enabled, then it will see this and initialize its DFU.
+ */
 void platform_request_boot(void)
 {
 	magic[0] = BOOTMAGIC0;
 	magic[1] = BOOTMAGIC1;
 	scb_reset_system();
 }
 
-#pragma GCC diagnostic pop
-
 #ifdef PLATFORM_HAS_POWER_SWITCH
 bool platform_target_get_power(void)
 {

src/platforms/common/blackpill-f4/usbdfu.c

@@ -46,9 +46,8 @@ int main(void)
 	if (!gpio_get(GPIOA, GPIO0) || (magic[0] == BOOTMAGIC0 && magic[1] == BOOTMAGIC1)) {
 		magic[0] = 0;
 		magic[1] = 0;
-	} else {
+	} else
 		dfu_jump_app_if_valid();
-	}
 
 	rcc_clock_setup_pll(&rcc_hse_25mhz_3v3[PLATFORM_CLOCK_FREQ]);