soc: mtk-pmic-wrap: avoid integer overflow warning

On ARM64, the mtk-pmic-wrap driver causes a harmless warning:

mtk-pmic-wrap.c:1062:16: warning: large integer implicitly truncated to unsigned type [-Woverflow]
mtk-pmic-wrap.c:1074:16: warning: large integer implicitly truncated to unsigned type [-Woverflow]
mtk-pmic-wrap.c:1086:16: warning: large integer implicitly truncated to unsigned type [-Woverflow]
  .int_en_all = ~(BIT(31) | BIT(1)),

The problem is that the result of the BIT() macro is an 'unsigned long',
so taking the bitwise NOT operation of that results in an integer
with the upper 32 bits all set and that cannot be assigned to a
'u32' variable without loss of information.

This is harmless because we were never interested in the upper bits
here anyway, so we can shut up the warning by adding a simple cast
to 'u32'.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>