power: reset: pwr-mlxbf: change rst_pwr_hid and low_pwr_hid from global to local variables

sparse reports
drivers/power/reset/pwr-mlxbf.c:19:12: warning: symbol 'rst_pwr_hid' was not declared. Should it be static?
drivers/power/reset/pwr-mlxbf.c:20:12: warning: symbol 'low_pwr_hid' was not declared. Should it be static?

Both rst_pwr_hid and low_pwr_hid are only used in a single function
so they should be local variables.

Fixes: a4c0094f ("power: reset: pwr-mlxbf: add BlueField SoC power control driver")
Signed-off-by: Tom Rix <trix@redhat.com>
Acked-by: Asmaa Mnebhi <asmaa@nvidia.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>