pinctrl: sh-pfc: Validate fixed-size field widths at build time

Add a build-time check, to ensure the register and field widths in
descriptors for config registers with fixed-width fields are sane.
This helps catching bugs early.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>

drivers/pinctrl/sh-pfc/sh_pfc.h

@@ -126,7 +126,8 @@ struct pinmux_cfg_reg {
  * one for each possible combination of the register field bit values.
  */
 #define PINMUX_CFG_REG(name, r, r_width, f_width) \
-	.reg = r, .reg_width = r_width, .field_width = f_width,		\
+	.reg = r, .reg_width = r_width,					\
+	.field_width = f_width + BUILD_BUG_ON_ZERO(r_width % f_width),	\
 	.enum_ids = (const u16 [(r_width / f_width) * (1 << f_width)])
 
 /*