configure: Fixed check for AM_PATH_LIBCCRYPT

Problem : Getting following build error when libgcrypt is not found:

configure.ac:1909: warning: macro 'AM_PATH_LIBGCRYPT' not found in library
configure.ac:1909: error: possibly undefined macro: AM_PATH_LIBGCRYPT
      If this token and others are legitimate, please use m4_pattern_allow.
      See the Autoconf documentation.

Solution: Fixed check for AM_PATH_LIBCCRYPT