net: ipa: use proper endpoint mask for suspend

It is now possible for a system to have more than 32 endpoints.  As
a result, registers related to endpoint suspend are parameterized,
with 32 endpoints represented in one more registers.

In ipa_interrupt_suspend_control(), the IPA_SUSPEND_EN register
offset is determined properly, but the bit mask used still assumes
the number of enpoints won't exceed 32.  This is a bug.  Fix it.

Fixes: f298ba78 ("net: ipa: add a parameter to suspend registers")
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>