ShellPkg: Fix ASCII input redirection does not work correctly.

ShellPkg: Fix ASCII input redirection does not work correctly.

When executing 'ls -b <a arg.txt' Shell cannot get the ASCII char in 'arg.txt' correctly.
This patch updates the file read buffer size when read from ASCII file to fix the bug.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Qiu Shumin <shumin.qiu@intel.com>
Signed-off-by: Felix Poludov <Felixp@ami.com>
Signed-off-by: Oleksiy Yakovlev <Oleksiyy@ami.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18609 6f19259b-4bc3-4df7-8a09-765794883524