Adjust tdsaContext_t::NvmdResponseSet declaration to avoid clang 15 warning

With clang 15, the following -Werror warnings are produced:

In file included from sys/dev/pms/freebsd/driver/ini/src/agtiapi.c:70:
sys/dev/pms/RefTisa/tisa/sassata/common/tdsatypes.h:346:13: error: type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int [-Wimplicit-int]
  volatile  NvmdResponseSet;
  ~~~~~~~~  ^
  int

The NvmdResponseSet member is effectively only used as a boolean in the
pms(4) driver, so it could be a single bit. But to avoid changing the
semantics at all in this unmaintained driver, simply declare it as a
volatile int.

MFC after: 3 days

(cherry picked from commit 95204d7a6368990e216db0ad51ef3e6018aed27c)