regmap: silence GCC warning

Building regmap.o triggers this GCC warning:
    drivers/base/regmap/regmap.c: In function ‘regmap_raw_read’:
    drivers/base/regmap/regmap.c:1172:6: warning: ‘ret’ may be used uninitialized in this function [-Wmaybe-uninitialized]

Long story short: Jakub Jelinek pointed out that there is a type
mismatch between 'num' in regmap_volatile_range() and 'val_count' in
regmap_raw_read(). And indeed, converting 'num' to the type of
'val_count' (ie, size_t) makes this warning go away.
Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/base/regmap/regmap.c

@@ -82,7 +82,7 @@ bool regmap_precious(struct regmap *map, unsigned int reg)
 }
 
 static bool regmap_volatile_range(struct regmap *map, unsigned int reg,
-	unsigned int num)
+	size_t num)
 {
 	unsigned int i;