bq24190_charger: Workaround SS definition problem on i386 builds

For __i386__ builds we have:

arch/x86/include/uapi/asm/ptrace-abi.h:#define SS   16

And in the driver:

BQ24190_SYSFS_FIELD_RO(vbus_stat,       SS,     VBUS_STAT)

That breaks the build like this:

drivers/power/bq24190_charger.c:375:138: error: ‘BQ24190_REG_16’
undeclared here (not in a function)
drivers/power/bq24190_charger.c:375:162: error:
‘BQ24190_REG_16_THERM_STAT_MASK’ undeclared here (not in a function)
drivers/power/bq24190_charger.c:375:203: error:
‘BQ24190_REG_16_THERM_STAT_SHIFT’ undeclared here (not
 in a function)

With this commit we workaround the problem by undefining 'SS'.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Anton Vorontsov <anton@enomsg.org>