uapi: fix linux/target_core_user.h userspace compilation errors

Consistently use types from linux/types.h to fix the following
linux/target_core_user.h userspace compilation errors:

/usr/include/linux/target_core_user.h:108:4: error: unknown type name 'uint32_t'
    uint32_t iov_cnt;
/usr/include/linux/target_core_user.h:109:4: error: unknown type name 'uint32_t'
    uint32_t iov_bidi_cnt;
/usr/include/linux/target_core_user.h:110:4: error: unknown type name 'uint32_t'
    uint32_t iov_dif_cnt;
/usr/include/linux/target_core_user.h:111:4: error: unknown type name 'uint64_t'
    uint64_t cdb_off;
/usr/include/linux/target_core_user.h:112:4: error: unknown type name 'uint64_t'
    uint64_t __pad1;
/usr/include/linux/target_core_user.h:113:4: error: unknown type name 'uint64_t'
    uint64_t __pad2;
/usr/include/linux/target_core_user.h:117:4: error: unknown type name 'uint8_t'
    uint8_t scsi_status;
/usr/include/linux/target_core_user.h:118:4: error: unknown type name 'uint8_t'
    uint8_t __pad1;
/usr/include/linux/target_core_user.h:119:4: error: unknown type name 'uint16_t'
    uint16_t __pad2;
/usr/include/linux/target_core_user.h:120:4: error: unknown type name 'uint32_t'
    uint32_t __pad3;

Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>