contrib/bpftrace: exec bpftrace, remove useless cat

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Pavel Zakharov <pavel.zakharov@delphix.com>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #11859

contrib/bpftrace/zfs-trace.sh

@@ -1,9 +1,9 @@
 #!/bin/sh
 
-ZVER=$(cat /sys/module/zfs/version | cut -f 1 -d '-')
+ZVER=$(cut -f 1 -d '-' /sys/module/zfs/version)
 KVER=$(uname -r)
 
-bpftrace \
+exec bpftrace \
 	--include "/usr/src/zfs-$ZVER/$KVER/zfs_config.h" \
 	-I "/usr/src/zfs-$ZVER/include" \
 	-I "/usr/src/zfs-$ZVER/include/spl" \