PM: EM: Remove unused parameter from em_adjust_new_capacity()

The max_cap parameter of em_adjust_new_capacity() is not used. Indeed,
the maximum capacity used as a reference to recompute performance
levels of the Energy Model is obtained in em_init_performance()
through arch_scale_cpu_capacity().
Remove the unused parameter.

The parameter is introduced in:
commit e3f1164f ("PM: EM: Support late CPUs booting and capacity adjustment")

Signed-off-by: Pierre Gondois <pierre.gondois@arm.com>