-ти, -ть, -чь are variations of the same infinitive suffix in complementary distribution: -ть is used when unstressed (да́ть, бра́ть), -ти when stressed (мести́, нести́), and -чь when the stem ending is a velar stop (к or г): печь (пеку), стричь (стригу) etc.
However, in poetic speech -ть and -ти (as well as -чь and now extinct -чи) are in free variation, dictated by rhythm, rhyme and meter:
Но ка́к / проне́сть / мне э́/тот во́/рох
Призна́/ний че́/рез ва́ш / поро́г?
Here, the iamb (two-syllable foot with the stress on the last syllable) requires пронесть to be a two-syllable oxytone (a word with the stress on the last syllable).
Дай к тебе́ нам, / по тебе́ нам, / мать, ступа́ти
В час вече́рний, / на моско́вском, / на Арба́те.
And here, the third paean (four-syllable foot with the stress on the third syllable) requires ступати to be a three-syllable paroxytone (a word with the stress on the penultimate syllable).
So, answering your question, ско́мкати is a poetic variation of the infinitive ско́мкать.