dm: mips: Fix lb60 timer code

dm: mips: Fix lb60 timer code

The timer code contains more halfword writes which trigger gcc errors.
The registers are again 32bit, yet written by 16bit writes, fix this:

timer.c: In function ‘reset_timer_masked’:
timer.c:37:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
timer.c: In function ‘get_timer_masked’:
timer.c:43:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
timer.c: In function ‘timer_init’:
timer.c:86:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
timer.c:88:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
timer.c:89:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
timer.c:90:2: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Daniel <zpxu@ingenic.cn>
Cc: Shinya Kuribayashi <skuribay@pobox.com>
Cc: Xiangfu Liu <xiangfu@openmobilefree.net>