catch None.get in BitPat.apply(x: UInt): BitPat (backport #2276) (#2296)

* catch None.get in BitPat.apply(x: UInt): BitPat (#2276)

Co-authored-by: Jack Koenig <koenig@sifive.com>
(cherry picked from commit 849d4a0b

)

# Conflicts:
#	src/test/scala/chiselTests/util/BitPatSpec.scala

* Resolve backport conflicts

Remove BitPatSpec since this backport is just a simple require.

Co-authored-by: Jiuyang Liu <liu@jiuyang.me>
Co-authored-by: Jack Koenig <koenig@sifive.com>