ioemu: Avoid struct members clashing with POSIX apis

ioemu: Avoid struct members clashing with POSIX apis

The TPM code in tools/ioemu/hw/tpm_tis.c has a struct containing a
number of function pointers with names open, close, read, write which
are the same as various POSIX apis already #included in the
file. POSIX allows these functions to be defined as macros and latest
GCC/glibc does indeed define them as macros depending on compiler
flags. This causes compile errors when deferencing the struct
members. The solution is either to change calls like   ctx->open () to
be (* ctx->open) (), or simply to rename the struct members. Since
this struct was only used inside that one file I simply renamed them.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>