regmap: pass buffer size to regmap_raw_read() in regcache_hw_init()

regcache_hw_init() uses regmap_raw_read() to initialize cache
when reg_defaults_raw isn't provided.

The last parameter to regmap_raw_read() is buffer size in bytes,
however regcache_hw_init() called it with number of registers
to read instead, which cause problem if they aren't one byte
wide in cache.

This wasn't triggered by any of current in-tree drivers
since they either have one-byte registers or provide
reg_defaults_raw explicitly.

Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Signed-off-by: Mark Brown <broonie@kernel.org>