bus: mhi: core: fix potential operator-precedence with BHI macros
The BHI_MSMHWID and BHI_OEMPKHASH macros take a value 'n' which is
a BHI register index. If 'n' is an expression rather than a simple
value, there can be an operator precedence issue which can result
in the incorrect calculation of the register offset. Adding
parentheses around the macro parameter can prevent such issues.